Method of forming honeycomb panel edges

ABSTRACT

A method of contour-forming the edge of honeycomb sandwich panel comprising the steps of cutting a slit through the edge portion of the honeycomb midway between and parallel to the outer sheets of the sandwich, inserting a hardened blade into the slit, crushing the honeycomb core and thereafter removing the blade prior to the stretch-forming operation. This provides a bearing surface between the cells attached to the inner and outer panel sheets which permits the outer sheet to act independently of the inner sheet and thus form to contour satisfactorily in the subsequent stretch-forming step. In the alternative when crushing is not desired the blade is left in the slit during the stretchforming operation to provide the slip surface between the inner and outer sheets.

ite Sites 1 Haggberg et all.

[ METHOD OF FORMHNG HUNEYCOMB PANEL EDGES [75] Inventors: Marvin D. aggberg, Los Alamitos;

lira K. llfiavanagh, Fullerton; Leonard R. Van iiorik, Long Beach, all of Calif.

[73] Assignee: McDonnell Dougias Corporation,

Santa Monica, Calif.

[22] Filed: Nov. 3, 1972 [21] Appl. No.: 303,484

[ 5] .ian. 15, 1974 2,833,003 5/1958 Bourne et a1. 52/620 [57] ABSTRACT A method of contour-forming the edge of honeycomb sandwich panel comprising the steps of cutting a slit through the edge portion of the honeycomb midway between and parallel to the outer sheets of the sandwich, inserting a hardened blade into the slit, crushing the honeycomb core and thereafter removing the blade prior to the stretch-forming operation. This provides a bearing surface between the cells attached to the inner and outer panel sheets which permits the outer sheet to act independently of the inner sheet and thus form to contour satisfactorily in the subsequent stretch-forming step. In the alternative when crushing is not desired the blade is left in the slit during the stretch-forming operation to provide the slip surface between the inner andtouter sheets.

41 Cia ims, SDrawing Figures PATENIEDJAN 1 5 am I 8 3. 785.788

/0 g Z0 /2 m i 3 LIEI IJII Hl lil H ll ll I I! m m 61 I I I K 1 METHOD OF FORMING HONEYCOMB PANEL EDGES BACKGROUND OF THE PRESENT INVENTION A method has been developed for the stretchforming of arcuate lightweight rigid honeycombtype panels by providing controlled elongation of both cover sheets of the panels being formed. This method is disclosed in patent application Ser. No. 263,861 filed June 19, 1972 for Method of Forming Honeycomb Panels and reference is made to that application for more information thereon. The practice of that invention prevented crippling of the panel in the forming operation in which a metal honeycomb panel was stretch contour-formed around a generally cylindrical or compound convex shape. However, it did not completely solve the problem of anti-elastic deformation. Anticlastic deformation has been defined as having curvature opposite each other at a given point: convex in one direction and concave in the other. I

SUMMARY OF THE PRESENT INVENTION In accordance with the'present invention, the problem of anti-elastic deformation, which occurs along the longitudinal edges, is solved by making a slot in the core material of the honeycomb panels along the longitudinal edges in a plane substantially parallel to the cover sheets and midway therebetween. A hardened steel blade is inserted into the slotted area. If the panel edge is to be crushed in order to facilitate its attachmerit to a structural member, this crushing is done prior to the removal of the inserted blade which provides a bearing support between the inner and outer cover sheets during the subsequent stretch-forming operation. The insert blade imparts ahoneycomb core flattened slip plane surface between the two edges of the slotted honeycomb panel during the panel edge crushing operation. If the final panel edge is not to be crushed, the blade is left inserted in the panel slotted edge during the subsequent stretch-forming operation, after which the blade insert is then removed. The insert bladeitself provides the required slip plane surface between the two raw edges of the slotted honeycomb panel. In both cases the undesirable anti-clastic defor mation during the subsequent required stretch-forming operation is nullified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a vertical elevational view of a honeycomb panel;

FIG. 2 is a vertical elevational view of a honeycomb panel having a slit along one edge thereof;

FIG. 3 is an elevational view of a honeycomb panel with a hardened steel blade inserted into the slotted area;

FIG. 4 shows an elevational view of a honeycomb panel with the edge thereof being crushed while the steel blade remains in the slotted area; and

FIG. 5 is an elevational view of a honeycomb panel fastened at the edge thereof to a structural member.

BRIEF DESCRIPTION OF ILLUSTRATIVE EMBODIMENT and 1 1. This panel may be of the type discussed in the previously referred-to patent application and, accordingly, further discussion is not deemed necessary. In an illustration of the method of the present invention, the problem is to bend this panel into an arcuate shapeand then fasten the edge 16 to a support member such as support member 18 in FIG. 5. In accordance with the present invention, a slit 20 is first cut in honeycomb core along the edge 16 of the panel. A width of approximately one-eighth inch has been found acceptable between the raw edges 22, 24 of the honeycomb forming the slot. A relatively thin hardened steel blade 26 on the order of 0.025 inch thickness is next inserted into the slot 20.

At this point in the panel forming operation a decision is necessary as to whether the edge of the panel is to be crushed in order that it may be fastened in the manner shown in FIG. 5, or whether the panel is simply to be curved through the stretch-forming techniques of the previously referred-to application without this crushing. Assuming the latter case, in which the stretch-forming operation is to be done but the edge 16 is not to be crushed, this blade 26 remains inserted within the slot 20 throughout the stretch-forming operation. The insert blade 26 provides the required slip plane surface between the two raw edges 22, 24 of the slotted honeycomb 10 and this bearing surfaceallows the outer skin or cover sheet 12 to slide relative to the 5 Reference is made to FIG. I wherein there is shown 6 an inner layer or core ll) of metal honeycomb sandwiched between the upper and lower cover sheets 12 inner sheet 14, resulting in a satisfactory contourforming and nullifying of the undesirable anti-elastic deformation during the subsequent stretch-forming operation.

In most cases in which the edge of the panel must be crushed to facilitate its attachment, such as to the support structure 18 in FIG. 5, for example, the insert 26 remains in slot 20 during the crushing operation. Die punch 28 and anvil 30 are symbolic of this crushing operation which may be done in a conventional manner. As the core 10 is crushed with the hardened insert 26 slid into the slot 20, The cells of core 10 are fiattened such that a bearing surface is created between core edges 22 and 24 to permit the outer sheet 12 to slide relative to the inner sheet 14 resulting in a satisfactory contour-forming of the panel.

An example of the finished product may be seen in FIG. 5. Here at edge 16 the inner and outer sheets 12 and 14 are shown pressed together with .the inner cellular core crushed between them. A cover plate or doubler 32 has a flange 34 curved over the end of the panel and serves as a backing. The cover plate extends beyond the depth of the slot 20. Bolts 36 retain the panel edge 16 and cover plate 32 to the support structure 18.

Having thus described an illustrative embodiment of the present invention, it is to be understood that modifications thereof will become apparent to those skilled in the art and that these deviations are to be constued as part of the present invention.

We claim:

1. The method of contour-forming a honeycomb sandwich panel having a pair of face sheets with a honeycomb core therebetween, said method comprising the steps of:

a. cutting a slit through the honeycomb core in a plane substantially parallel to and equi-distant from the face sheets of thepanel,

3. The method of contour-forming a honeycomb sandwich panel as in claim 1 wherein the edge of the panel having said slit with said blade therein is crushed to flatten the honeycomb raw edges defining said slit against said blade to provide a slip plane bearing surface which permits relative movement of said face sheets at said edge during subsequent stretching of said panel over said form.

4. The method of contour-forming a honeycomb panel as in claim 1 wherein both said face sheets are stretched as said panel is bent over said form. 

1. The method of contour-forming a honeycomb sandwich panel having a pair of face sheets with a honeycomb core therebetween, said method comprising the steps of: a. cutting a slit through the honeycomb core in a plane substantially parallel to and equi-distant from the face sheets of the panel, b. inserting a relatively thin hard blade in said slit to provide a bearing surface for the adjacent honeycomb edges defined by said slit, c. stretching and bending said panel over a form to provide said pAnel with a desired contour, and d. removing said blade from said slit.
 2. The method of contour-forming a honeycomb sandwich panel as in claim 1 wherein said blade provides a slip plane surface for relative movement of the honeycomb raw edges defining said slit on either side of said blade as said panel is being stretched over said form.
 3. The method of contour-forming a honeycomb sandwich panel as in claim 1 wherein the edge of the panel having said slit with said blade therein is crushed to flatten the honeycomb raw edges defining said slit against said blade to provide a slip plane bearing surface which permits relative movement of said face sheets at said edge during subsequent stretching of said panel over said form.
 4. The method of contour-forming a honeycomb panel as in claim 1 wherein both said face sheets are stretched as said panel is bent over said form. 